A micron-spined reference for sharpening media
This began with a question we kept being asked: a friend wanting to know whether a #1000 waterstone is really finer than a 600 diamond plate, a customer asking where the ZenSharp cards fall next to the stones already on their bench. There was no single place to look it up, because a grit number means something different from one maker to the next. So we built one.
One axis, the size of the particle that actually cuts. Particle size in microns is the one physical measure every abrasive shares. The grit number printed on a stone is a label, and across makers the two do not always agree. This table places every medium on that one axis and stays honest about two things: how sure we are of a number, and how wide the abrasive really is.
A micron is one millionth of a meter, one thousandth of a millimeter. It is the unit abrasives are actually measured in, because a grit number is only a label and the micron is the thing. The coarsest grinding grit here is wider than a human hair; the finest polishing abrasive is about half a micron, finer than the wavelength of visible light, which is why a polished bevel turns to a mirror: the scratches left behind are smaller than light can resolve.
Drawn to one true scale, coarse on the left, fine on the right. The very coarsest and very finest grades are left off (at true scale one would dwarf the rest and the other would vanish); the size table below lists the full range.
Everyday sizes are typical figures (a human hair runs roughly 50 to 100 microns, pollen 10 to 100): a sense of scale, not an exact measurement.
An abrasive is never a single size. It is a spread of sizes around a median, and that is the second thing this table tracks, alongside how sure we are of a number. Two stones can share the same median grit and still cut differently: one holds a tight spread, the other a wide one. A wide spread carries stray coarse grains that scratch deeper than the number promises; a tight spread cuts more evenly and finishes finer.
a wide spread
a tight spread
Same median, different spread. Both clusters average about the same size; the left runs from fine to coarse, the right stays close to one size. Where a maker or standard publishes the distribution we draw it as a band; otherwise a point, and we say the spread is unknown.
Particle size is one dimension, the one that fits on a single scale. It is not the whole of how an abrasive behaves. The mineral matters: aluminium oxide, silicon carbide, diamond, and CBN cut differently at the same micron. So does how the grain holds up, whether it fractures to keep a fresh edge or rounds over and burnishes, how hard it is against the steel, and the shape of the edge it leaves. Two abrasives can share a micron and still feel nothing alike at the bench. This table maps the size; the rest is yours to learn by using them.
Our one design choice
A common scale to read every grit number against
A grit number is not a measurement. P400 sandpaper, a #400 waterstone, and a 400-mesh diamond plate are three different sizes, and even two #1000 waterstones from different makers rarely agree. No single standard covers all of them, so to read one product against another the table needs one shared yardstick, and we had to choose it.
We use JIS R6001, the Japanese microgrit standard. It spans the widest range sharpening actually uses (#240 to #8000), defines each grade by a measured distribution rather than a single number, and its numbers are the ones most waterstones already reach for. We fit a smooth curve through its grades so any number maps to a micron, and extend past its ends by continuing the standard's own trend, marked uncertain because no standard defines those grades. It is not a new standard and does not replace JIS or ISO. It is a reading aid: one place to ask where a grit number actually lands. Every product page shows that equivalent.
335 entries across 56 lines. 111 standard-defined, 137 maker-published, 84 estimated. Only 133 carry a published distribution; the other 202 are single points, the spread unknown. The bar on each line shows that mix, firm ink to faded.
An open invitation
If you make the grit, help us measure it
If you manufacture or sell a sharpening abrasive, we would like your measured particle-size data: a median in microns, the distribution if you have one, and the method behind it. We will list it as maker-published, cite you by name, and correct anything we have shown wrong. A reference is only as good as its sources, and the best source for a grade is the people who grade it.